With increasing bandwidths available on fiber optic communication paths, information providers can now deliver a broader range of information, e.g., high definition video, to a subscriber premises. However, even with advancements in optical fiber telecommunication technology, theft of services remains a growing concern among information providers (e.g., cable television service providers). The problem involves the fact that once a central station distributes signals in a general manner to a subscriber premises, the central station loses control of the signals. As a result, such signals are exposed to theft which results in lost revenue.
Presently, one approach to remedy the service theft problem is to transmit scrambled signals or channels to each subscriber's premises. Each subscriber premises is equipped with a smart set top box to descramble those signals or channels ordered by the subscriber. Such systems however require additional equipment, specifically scramblers and descramblers, which increases their overall cost. Moreover, intelligent set top boxes that permit theft of services are presently available on the black market. Such set top boxes can descramble all scrambled signals transmitted to the subscriber premises, thereby allowing the subscriber access to those signals or channels.
Another approach to remedy the service theft problem is found in U.S. Pat. No. 4,994,909 (hereafter referred to as “the Graves patent”). The Graves patent provides a video signal distribution system (hereafter “the Graves system”) that includes a services switching device and an optical network interface (ONI) for selecting particular signals for delivery to a subscriber. The services switching device employs multiplexers for producing time-division multiplexed (TDM) signals. Because the processing and routing of TOM signals is typically accomplished utilizing electronics, a drawback of the Graves system is a need for optical-to-electrical and electrical-to-optical conversions and for controlled environmental vaults, power back-ups and maintenance.
Another multi/demultiplexing technique that employs optical rather than electrical multiplexing, is wavelength division multiplexing (WDM). WDM provides significant advantages over TDM. Specifically, wavelength multiplexed channels can be separated and combined passively, independent of the format and bit rate of the data being transferred. An example of a fiber optic subscriber loop architecture utilizing WDMs is found in U.S. Pat. No. 5,221,983 (hereafter referred to as “the Wagner patent”). However, such subscriber-type systems employing WDMs neither provide nor suggest any mechanism for selecting particular signals for delivery to a subscriber premises.
Accordingly, it is an object of the system (disclosed in the “related applications” referenced above) in which the present invention may be used, to provide a fiber optic subscriber loop architecture, based on WDM techniques, which can selectively transmit only those bands ordered by the subscriber to the subscriber premises.
A further object of the system (disclosed in the “related applications” referenced above) in which the present invention may be used, is to eliminate the need for scramblers and descramblers at the subscriber premises and, thus, reduce the overall cost of the system.
Another object of the system (disclosed in the “related applications” referenced above) in which the present invention may be used, is to prevent theft of information services.
Besides the aforementioned shortcomings and limitations of the prior art, the system (disclosed in the “related applications” referenced above) in which the present invention may be used also overcomes limitations and deficiencies relating to wideband transmission to the subscriber premises, especially wideband digital services. In providing these services, the information destined for the subscribers is digitally encoded, typically using the MPEG or MPEG-2 (Moving Pictures Experts Group) standards, and propagate as a digital stream over the transmission medium. (Digital encoding (or compression) is deployed to effectively utilize the bandwidth of the communications medium.) If front-end encoding is used, the receiver at each customer premises requires digital decoder to reconstruct the original information. Moreover, if two-way or bi-directional communication is desired, then the equipment at the customer premises may be arranged with a digital encoder. The decoding/encoding required by the customer's equipment is expensive. Moreover, it is virtually impossible with such an arrangement to deliver tailored services, that is, subscriber-dependent services, to each individual subscriber.
To overcome the limitations of encoded digital propagation, some recently devised systems focus on non-encoding propagation so that that subscriber's TV may be used in the conventional manner to receive the transmitted signals. Representative of such technology using a single-fiber for a transmission medium is a system for propagating a plurality of downstream video channels over the single fiber in combination with two-way interactive telephony communications over the same fiber, as disclosed in the article, H. Ogura et al, “Launch of ‘CATV Video Distribution Service’ over FTTH”, NTT Review, Vol. 9, No. 6 (November 1997) (hereafter referred to as “the Ogura article”). As described in the Ogura article, two or more communications channels are delivered over a single optical fiber from a head-end to a subscriber's home to effect fiber-to-the-home (FTTH) service. In general, the design philosophy for the system discussed in the Ogura article (hereafter referred to as “the Ogura system”) is one of the separating downstream video from interactive, non-video communications; that is, propagating the downstream video at one wavelength (namely, 1.5 micrometers) and the interactive telephony communications at the second wavelength (namely, 1.3 micrometers). Moreover, this bi-directional telephony arrangement uses TCM (time compression multiplexing) in the so-called “ping-pong” communication mode, wherein all downstream receivers detect the same signal, and each upstream communication from a given subscriber is assigned a unique time slot.
In particular, in the Ogura system, connections from the head-end to each of the customers fans-out. Consequently, every customer receives the same downstream signal broadcast from the head-end. That is, there is no ability to deliver to a given subscriber selected ones of the video channels composing the propagated downstream signal. Such an arrangement is typically referred to as a “tree-and-branch” delivery system. Consequently, there is the potential for theft of the services as alluded to above. In addition, to derive the signal for the subscriber, a number of signal splitters are deployed. Consequently, the signal delivered to front-end of the cascade of splitters must have a high power level. This is disadvantageous since high power components tend to be more costly.
Moreover, the Ogura system was designed to be implemented on already existing 1.3 micrometer zero-dispersion fibers to reduce implementation costs, but the downstream video utilizes the 1.5 micrometer wavelength for propagation. When a 1.5 micrometer optical wavelength is transmitted through a 1.3 micrometer zero-dispersion fiber, fiber dispersion induces a degradation with a concomitant deterioration in signal (e.g., video signal) quality. Consequently, the Ogura system must be arranged with dispersion compensation, which adds to its complexity and cost.
Also, the types of interactive services taught or suggested by the Ogura article are existing services such as plain old telephone service (POTS) and narrowband ISDN. There is no teaching or suggestion of using the interactive services part of the Ogura system (1.3 micrometer wavelength) for video, especially video conferencing, or wideband data. In brief, the Ogura system separates video (downstream at 1.5 micrometers) from telephony (upstream and downstream at 1.3 micrometers) using a tree-and-branch delivery system for downstream transmission. This is, in contrast to the present inventive subject matter, wherein the wavelength assignments are characterized as separating downstream from upstream, irrespective of the content of the downstream or upstream signals, and the system is arranged as a “star-delivery” system.
Still another object of the system (disclosed in the “related applications” referenced above) in which the present invention may be used is, to house environmentally sensitive components in well-controlled environments such as a central office or a customer's premises.
Yet another object of the system (disclosed in the “related applications” referenced above) in which the present invention may be used to provide “star-delivery” system between the central location and each customers premises.